This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The purpose of this study is to investigate the efficacy and safety of adefovir dipivoxil for the treatment of chronic hepatitis B in children and adolescents (age 2 to 18) compared to placebo following 48 weeks of treatment;To evaluate the proportion of children and adolescents who experience HBeAg and HBsAg seroconversion following 48 weeks of treatment with adefovir dipivoxil or placebo;To evaluate the development of HBV mutants resistant to adefovir dipivoxil; To evaluate the long-term safety and efficacy in children and adolescents over an additional 4 year follow up period including assessment of growth and renal function. The common side effects were weakness, headache, stomach pain, nausea, gas, diarrhea, and upset stomach. some patients with advanced chronic hepatitis B liver disease and impaired kidney function, taking adefovir dipivoxil 10 mg caused nephrotoxicity. In children, complants of headache and dizziness were generally mild, and did not appear to be related to dose. The primary endpoint analysis will be performed when all patients reach the week 48 study visit. The adefovir dipivoxil treatment group will be compared to the placebo treatment group with respect to all efficacy endpoints. The intent to treat (ITT) population will be used for these analyses. The primary analysis will be performed on the intent-to-treat population.